/Engine/Source/Editor/GraphEditor/Public/SNodePanel.h
Panels arrange their children in a space described by the AllottedGeometry parameter. The results of the arrangement should be returned by appending aFArrangedWidgetpair for every child widget. See StackPanel for an example
virtual void OnArrangeChildren &40; const FGeometry & AllottedGeometry, FArrangedChildren & ArrangedChildren &41; const